These guide rails are made of high-grade, solid plastic and allow aquarium cover plates to be simply and conveniently slid to the side. This makes feeding, changing the water and any kind of maintenance task on the aquarium much easier. The guide rails are suitable for 4 mm glass panes and are ideally placed onto the longitudinal struts of your aquarium. You do not have to hold them in place with glue. They are easily cut to length with a simple handsaw. Please note that you will require 2 guide rails per cover!